I have had a support ticket open about this for 8 months now, but support refuse to reply to my emails.
I have the pro version of Zoiper IAX
It constantly keeps disconnecting and saying "registering" and I have to keep restarting the app.
I have already tried all solutions, the app is excluded from all battery saver settings.
It is set to run in background and to autostart.
I have had the same issue on 3 different phones.
Also recently when I get a call, I can hear it ringing, but there is no way to answer the call, as nothing pops up. Even if I manually open the app, still no way to answer the call.
My current phone Is a POCO X6 pro